1. Field of the Invention
This invention relates to form-fill-seal wrapping apparatus, an example being the machine currently sold by the present applicant under the Registered Trade Mark FLOWPAK and the designation RF 255 FLOWPAK.
2. Description of the Prior Art
In each task assigned to it, the apparatus is required to wrap a succession of items which are nominally the same size. It is a feature of such apparatus that it is fitted with product size change settings which can be changed to allow items of nominally different sizes to be wrapped.
Changing settings from one wrapping task to another involves considerable effort on the user's behalf. As will become apparent hereinbelow, a simple product size change, i.e. doubling the length of the items which are to be wrapped, involves changes in speed of some machine drives but no changes in others. Those that are changed are unlikely to be changed by a simple factor.
To establish synchronism of the machine elements in the aftermath of such changes, it is conventional to provide the wrapping apparatus with mechanical drives which incorporate differential gearing, these permitting not only a setting up of the machine so that all the drives are synchronised but, also, a fine adjustment of the synchronism during routine operation of the machine.
However such differentials are complex, comprise a multiplicity of parts and are expensive to manufacture.
Changing from one wrapping task to another has hitherto been an operation performed by a technician or engineer. It is one object of the present invention to simplify the wrapping task changing procedure to such an extent that it is feasible for it to be accomplished by personnel who operate the apparatus during the wrapping tasks.
The previously proposed horizontal form-fill-seal wrapping machines employ a pair of rotary sealing jaws to effect transverse sealing of the wrapper web between successive sealing of the wrapped product items. The present inventor is aware that a sealing jaw speed which is markedly different from the wrapper speed, during the portion of the jaw cycle when the jaws are sealing together the two overlaid sheets of wrapping material, will adversely affect the seal quality. He is also aware that it is necessary to ensure that the jaws not only rotate in synchronism with the wrapping cycle but also move at substantially the speed of advance of the wrapping web during the sealing portion of the cycle, which speed will change with each wrapping task even if, in each of these tasks, the same number of items are wrapped per unit of time. Accordingly, it is another object of the present invention so to modulate the rotation of the sealing jaws that the successive product items are spaced closely together and the seal quality is not adversely affected by a speed discrepancy, as mentioned above, throughout the duration of a range of different wrapping tasks.